1. Field of the Invention
The present invention relates generally to the field of cooled optical elements. More specifically, the present invention relates to optical elements having a transparent substrate with coolant circulating through a series of cooling channels extending through the substrate across at least one face of the element.
2. Statement of the Problem
When exposed to a high-power beam of radiation, optical elements are subjected to extreme thermal loads causing distortion in the reflective or refractive surfaces. A number of devices and processes have been invented in the past relating to cooling of mirrors, lens, and other optical elements in high power applications, including the following:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Sorensen, et al. 3,708,223 Jan. 2, 1973 Brubaker, et al. 4,057,332 Nov. 8, 1977 Stalcup, et al. 4,221,469 Sept. 9, 1980 Eitel 4,378,626 April 5, 1983 Mahawili 4,550,684 Nov. 5, 1985 Thompson, et al. 4,657,359 Apr. 14, 1987 Mahawili 4,680,447 July 14, 1987 Marmo, et al. 4,740,276 Apr. 26, 1988 ______________________________________
Sorensen, et al., disclose a basic example of a cooled mirror in which a series of passages located behind the reflective surface circulate a coolant to minimize thermal distortion of the mirror.
Stalcup, et al., disclose a thermally stabilized mirror in which circulation of coolant in channels behind the face plate of the mirror is used to induce a thermal stress within the back plate of the device. This is done to balance bending stresses produced within the face plate by thermal growth resulting from heat generated by incident radiation.
Eitel, Thompson, et al., and Marmo, et al, disclose other variations of mirrors with cooling channels located behind the reflective surfaces.
Brubaker, et al, disclose a peripherally cooled lens assembly.
In U.S. Pat. Nos. 4,550,684 and 4,680,447, Mahawili discloses a device for heating semiconductor wafers by electromagnetic radiation. The radiation is directed from a lamp source onto the silicon wafer through a window constructed of two spaced-apart plates. Water is pumped through the space between these plates to control the window temperature.
3. Solution to the Problem
None of these prior art references shows an optical element having performance characteristics comparable to the present invention. These advantageous characteristics are largely due to the structure of the present invention wherein a grid of cooling channels extends through a transmissive substrate. As is discussed at length below, use of a transmissive substrate greatly reduces the thermal load placed on the coolant circulating through the grid of cooling channels.